It has been known that the chelate of copper (II) with 8-hydroxyquinoline, hereinafter referred to as copper oxinate, possesses biocidal properties and is useful as a fungicide in the treatment of cereal seeds and is also suitable for protecting plants. The advantages of copper oxinate include being non-irritating, possessing very low toxicity, almost zero volatility, high stability and can be prepared without any ecological problems.
The copper oxinate currently marketed possesses valuable activity against fusarium diseases, glume blotch and bunt; however, its activity against leaf stripe of barley is rather low. It is one of the objects of the present invention to find a compound possessing all the advantages of copper oxinate, but also possessing a broad activity spectrum with a high level of efficacy.
It has also been known that copper oxinate is a polymorphous compound, i.e. it has various crystalline forms, see Palenik, Acta. Cryst., 1964, 17(6), 687-695 and Suito, et al., Kolloid-z.z. Polym., 1966, 212(2), 155-161. Seven crystalline forms of copper oxinate have been reported, namely .alpha., .alpha.', .beta., .beta.', .beta.", .gamma. and .gamma.' forms. The .alpha., .alpha.', .gamma. and .gamma.' forms are considered as laboratory curiosities, while the .beta. form is the most stable under normal conditions in which copper oxinate is used.
It has been found that the .beta.' form of copper oxinate, considered to be unstable and to be a transition form between the .beta. form, which is stable under normal conditions, and the .beta." form, which is stable at higher temperatures, in fact possesses a broader activity spectrum than the .beta. form and exhibits enhanced efficacy as an antifungal agent.